[POC] Experiment with bundle analyzer CLI

[AbhiPrasad]

This is an experiment around #123 - opening a PR to brainstorm about the general approach.

The magic is at packages/bundle-analyzer/src/analyze.ts, which is used called by examples/plain-js/package.json via pnpm run analyze-bundle.

The problem here is that rollup is designed to work with ES modules, so it will always adds a slight transform when looking at CJS. This means the sizes are not fully accurate - but the trends over time (deltas) should be for each of the entrypoints (which are defined by your package.json).

Example stats:

{
  "version": "1",
  "bundleName": "example-rollup-bundle-cjs",
  "plugin": {
    "name": "codecov-rollup-bundle-analysis-plugin",
    "version": "1.0.0"
  },
  "builtAt": 1707794665814,
  "duration": 38,
  "bundler": { "name": "rollup", "version": "4.10.0" },
  "assets": [
    { "name": "main.js", "size": 354, "normalized": "main.js" },
    { "name": "a.js", "size": 234, "normalized": "a.js" },
    { "name": "b.js", "size": 333, "normalized": "b.js" },
    { "name": "c.js", "size": 333, "normalized": "c.js" },
    {
      "name": "common-BUKucrYi.js",
      "size": 123,
      "normalized": "common-BUKucrYi.js"
    },
    {
      "name": "_commonjsHelpers-CFO10eej.js",
      "size": 216,
      "normalized": "_commonjsHelpers-CFO10eej.js"
    }
  ],
  "chunks": [
    {
      "id": "main",
      "uniqueId": "0-main",
      "entry": true,
      "initial": false,
      "files": ["main.js"],
      "names": ["main"]
    },
    {
      "id": "a",
      "uniqueId": "1-a",
      "entry": true,
      "initial": false,
      "files": ["a.js"],
      "names": ["a"]
    },
    {
      "id": "b",
      "uniqueId": "2-b",
      "entry": true,
      "initial": false,
      "files": ["b.js"],
      "names": ["b"]
    },
    {
      "id": "c",
      "uniqueId": "3-c",
      "entry": true,
      "initial": false,
      "files": ["c.js"],
      "names": ["c"]
    },
    {
      "id": "common",
      "uniqueId": "4-common",
      "entry": false,
      "initial": false,
      "files": ["common-BUKucrYi.js"],
      "names": ["common"]
    },
    {
      "id": "_commonjsHelpers",
      "uniqueId": "5-_commonjsHelpers",
      "entry": false,
      "initial": false,
      "files": ["_commonjsHelpers-CFO10eej.js"],
      "names": ["_commonjsHelpers"]
    }
  ],
  "modules": [
    { "name": "./src/main.js", "size": 197, "chunkUniqueIds": ["0-main"] },
    {
      "name": "./src/main.js?commonjs-entry",
      "size": 0,
      "chunkUniqueIds": ["0-main"]
    },
    { "name": "./a.js", "size": 128, "chunkUniqueIds": ["1-a"] },
    { "name": "./a.js?commonjs-entry", "size": 0, "chunkUniqueIds": ["1-a"] },
    { "name": "./src/b.js", "size": 179, "chunkUniqueIds": ["2-b"] },
    {
      "name": "./src/b.js?commonjs-entry",
      "size": 0,
      "chunkUniqueIds": ["2-b"]
    },
    { "name": "./src/c.js", "size": 179, "chunkUniqueIds": ["3-c"] },
    {
      "name": "./src/c.js?commonjs-entry",
      "size": 0,
      "chunkUniqueIds": ["3-c"]
    },
    { "name": "./src/common.js", "size": 77, "chunkUniqueIds": ["4-common"] },
    {
      "name": "./commonjsHelpers.js",
      "size": 140,
      "chunkUniqueIds": ["5-_commonjsHelpers"]
    }
  ],
  "outputPath": "kappa"
}

We need to do some further processing of this stats file to remove entries that you don't care about (aka only focus on entry points).